Previous three-dimensional range imaging systems typically illuminate a target with a modulated monochromatic light source (e.g. a laser) and determine range to the target by a comparison of multiple images of the intensity distribution of modulated back scattered light received by an array detector, wherein each image corresponds to a unique phase delay being applied to the modulated monochromatic illumination. See for example, U.S. Pat. Nos. 4,935,616 and 6,088,086 and U.S. patent application Ser. No. 11/477,248 the entirety of each of which is hereby incorporated by reference. Other three-dimensional imaging systems may incorporate more than one monochromatic light source, but again range information is determined by separately (e.g. sequentially) illuminating the target with a given wavelength and determining range values based upon multiple images of received intensity distributions for that wavelength of the illumination source. These systems typically illuminate a scene serially with light sources of various wavelengths to “see through” clutter or ground cover. See for example, Johnson et al., “Adaptive LADAR Receiver for Multispectral Imaging”, Proceedings of SPIE, Vol. 4377 (2001). These approaches are necessarily restricted to determining range information by processing multiple monochromatic images of a given wavelength of backscattered illumination of the target, and typically require obtaining a separate “color” image of the target for textural information.
The present invention overcomes these limitations by simultaneously illuminating a target with at least three wavelengths of light (i.e. not monochromatic illumination) and determining range information based upon the collective processing of the obtained “color” images. In embodiments of the present invention, a target is illuminated with at least three wavelengths of light, each wavelength being loss modulated and having an impressed phase delay, wherein backscattered light from the target is loss demodulated and received by an array detector and converted to an electrical signal for each wavelength of illumination, wherefrom information related to the demodulated intensity distributions of each of the separate wavelengths is combined to determine the range to the target, on a point by point (e.g. pixel by pixel) basis. For embodiments utilizing illumination wavelengths within the visible spectrum, a “true color” image of the target as well as range information can be obtained from two images of the target. A “3D” image of the target can comprise a color image of the target supplemented with topographical (i.e. range) information. The present invention additionally allows for using inexpensive, commercially available light sources and array detectors, such as a xenon flash lamps and color CCD (charge coupled device) imagers. The present invention is suitable to applications including facial recognition, industrial inspection and measurement, robotic vision, collision avoidance, automated rendezvous and docking and, high speed three dimensional (3D) target imaging.